In the production of fluids from oil wells, it is general practice to utilize submergible pumping equipment when the subsurface formation pressure has fallen to a level at which some flow of well liquids to the surface occurs but said pressure is insufficient to bring the well liquids to the surface at the desired product rate. One type of pumping unit now in use is the submergible pump which is lowered into the well and which operates beneath the surface of the liquid, being powered by an electric motor.
Since formation pressure is adequate to produce some flow to the surface without the pumping unit, it is necessary to control the well and protect against blowout during the running in and removal of the pumping unit from the well. Such control and protection of the well is accomplished with safety systems which include various types of subsurface safety valves. Most subsurface safety valves are designed to control the fluid flow through a tubing string but in some instances the safety valve controls fluid flow in the annulus formed between the usual well casing and well tubing. This latter type is frequently referred to as an "annular" or poppet-type safety valve and one example of such valve is shown in U.S. Pat. No. 4,049,052.
Examples of prior art submergible pump installations including safety systems which utilize subsurface safety valves are disclosed in many prior patents and of particular interest are the installations and safety systems shown in prior U.S. Pat. Nos. 3,853,430, 4,121,659, 4,128,127 and 4,134,453.
In certain of such prior systems, the main subsurface safety valve is hydraulically controlled by the pump discharge pressure so that when the pump is operating, the valve is open; when pump operation ceases, the safety valve automatically closes. Pressure communication between the pump and the safety valve has heretofore been accomplished through the housing or jacket of the pump and this has made it necessary to physically connect the safety valve directly with the pump. As a result, removal of the pump from the well also removes the valve with the result that the well is left unprotected with no safety valve. U.S. Pat. Nos. 4,134,454 and 4,128,127 illustrate this type of arrangement.
In order to provide some means of shutting the well in so that the pumping equipment and safety valve may be removed, the prior U.S. Pat. No. 4,121,659 adds a second valve which is independently mounted in the well tubing below the pump and the hydraulically controlled safety valve. Although not physically connected to the pump, this second or foot valve must be opened during the pumping operation and opening is accomplished mechanically by means of a prong which extends downwardly from the pump-safety valve assembly. When such pump-safety valve assembly is removed from the well, the prong disengages the foot valve to permit its closure by spring force. In this type of installation, the second or foot valve is essential and since it is mechanically controlled, it must be located relatively close to the pump unit.
Also in those prior systems which utilize the pump discharge pressure for actuating the safety valve, the internal passages which establish communication between the pump unit and the safety valve are relatively small in volume and, therefore, it becomes necessary to employ an accumulator in order to provide sufficient liquid volume for developing immediate pressure to open said safety valve. Such accumulator, together with the structure required to conduct the pressure from the pump, then through a swivel or articulated joint, and finally to the safety valve, results in a complex and expensive assembly.